Add tests for the datetime C API

[pganssle]

BPO	36782
Nosy	@vstinner, @ericvw, @Mariatta, @pganssle, @tonybaloney, @SimiCode
PRs	bpo-36782: Created C API wrappers and added missing tests for functions in the PyDateTimeAPI. #13088

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/Mariatta'
closed_at = <Date 2019-05-27.23:36:05.321>
created_at = <Date 2019-05-03.13:46:57.506>
labels = ['easy', '3.8', 'type-feature', 'tests']
title = 'Add tests for the datetime C API'
updated_at = <Date 2019-05-27.23:36:05.316>
user = 'https://github.com/pganssle'

bugs.python.org fields:

activity = <Date 2019-05-27.23:36:05.316>
actor = 'vstinner'
assignee = 'Mariatta'
closed = True
closed_date = <Date 2019-05-27.23:36:05.321>
closer = 'vstinner'
components = ['Tests']
creation = <Date 2019-05-03.13:46:57.506>
creator = 'p-ganssle'
dependencies = []
files = []
hgrepos = []
issue_num = 36782
keywords = ['patch', 'easy']
message_count = 9.0
messages = ['341336', '341346', '341400', '341408', '341497', '341673', '341674', '342761', '343705']
nosy_count = 6.0
nosy_names = ['vstinner', 'ericvw', 'Mariatta', 'p-ganssle', 'anthony shaw', 'edison.abahurire']
pr_nums = ['13088']
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue36782'
versions = ['Python 3.8']

[pganssle]

A decent fraction of the datetime C API has no tests. If we had tests, we could have prevented bpo bpo-36025, which was a regression in the FromTimestamp method.

I would like to open this issue to suggest the addition of tests for the full interface, to prevent further regressions here.

To write a test, first add a wrapper function in the _testcapimodule module: https://github.com/python/cpython/blob/master/Modules/_testcapimodule.c#L2218

Then test that function here: https://github.com/python/cpython/blob/master/Lib/test/datetimetester.py#L5821

See an example at GH PR 11922: #11922

I recommend testing *both* the version of the function accessed by the Macro (e.g. PyDate_FromTimestamp) and from the C API capsule (e.g. PyDateTimeApi->FromTimestamp), since projects access these functions in both ways.

C API Documentation is here: https://docs.python.org/3/c-api/datetime.html

Currently untested:

• PyDate_FromDate / PyDateTimeAPI->Date_FromDate
• PyDateTime_FromDateAndTime / PyDateTimeAPI->DateTime_FromDateAndTime
• PyDateTime_FromDateAndTimeAndFold / PyDateTimeAPI->DateTime_FromDateAndTimeAndFold
• PyTime_FromTime -> PyDateTimeAPI->Time_FromTime
• PyTime_FromTimeAndFold -> PyDateTime->Time_FromTimeAndFold
• PyDelta_FromDSU / PyDateTime->Delta_FromDelta

Untested macros with no corresponding API module:

• PyDateTime_DATE_GET_YEAR

• PyDateTime_DATE_GET_MONTH

• PyDateTime_DATE_GET_DAY

• PyDateTime_DATE_GET_HOUR

• PyDateTime_DATE_GET_MINUTE

• PyDateTime_DATE_GET_SECOND

• PyDateTime_DATE_GET_MICROSECOND

• PyDateTime_DELTA_GET_DAYS

• PyDateTime_DELTA_GET_SECONDS

• PyDateTime_DELTA_GET_MICROSECONDS

I can spawn smaller issues for this if that's preferred, but I figured we'd start with this big meta-issue.

[pganssle]

This ticket should be reserved for the mentored sprint.

[tonybaloney]

Reserving this issue (in mentored sprint)

[simicode]

I have done PyDate_FromDate in #57297

[simicode]

I have done PyDateTime_FromDateAndTime. I'm moving on to add PyDateTime_FromDateAndTimeAndFold (plus documentation for fold as requested in https://bugs.python.org/issue36783) before making a PR.

[simicode]

I have submitted PR (under review) for these tests:

• PyDate_FromDate / PyDateTimeAPI->Date_FromDate
• PyDateTime_FromDateAndTime / PyDateTimeAPI->DateTime_FromDateAndTime
• PyDateTime_FromDateAndTimeAndFold / PyDateTimeAPI->DateTime_FromDateAndTimeAndFold
• PyTime_FromTime -> PyDateTimeAPI->Time_FromTime
• PyTime_FromTimeAndFold -> PyDateTime->Time_FromTimeAndFold
• PyDelta_FromDSU / PyDateTime->Delta_FromDelta

[simicode]

@p-ganssle
Please open a new bpo for the Untested macros. I will be happy to work on that in the sprints tomorrow.

[vstinner]

New changeset 98ff4d5 by Victor Stinner (Edison A) in branch 'master':
bpo-36782: Created C API wrappers and added missing tests for functions in the PyDateTimeAPI. (bpo-13088)
98ff4d5

[vstinner]

Paul Ganssle is in favor of backporting new tests to Python 3.7:
#13088 (comment)

But automated backports failed with a conflict. If someone wants to backport it manually, please go ahead!

In the meanwhile, I close the issue.